In military applications, two types of towed vehicles are well-known and often used for weapon gunnery practice and aircraft protection. These are aerial towed targets and aerial towed decoys, respectively. Aerial towed targets are typically towed behind an aircraft and used in conjunction with pilot weapon training exercises. Aerial towed decoys are typically used to draw various types of guided weapons away from an aircraft that the weapons are intended to destroy and/or used to evaluate effectiveness of guided weapon systems. Examples of an aerial target and aerial decoy are shown in United States Letters Patent Nos. 4,205,848 to Smith et al. and 4,852,455 to Brum, respectively.
Both aerial towed targets and decoys typically include electronic devices and circuitry incorporated therein. In this respect, aerial towed targets include various electronic devices which are used for purposes of scoring the pilot's performance during a training exercise. The decoys contain various types of electronic circuits which are operable to create an apparent target to a weapon to attract the weapon to the decoy, rather than the aircraft. One such electronic device is a transponder which is adapted to receive radar signals and re-broadcast an amplified return signal. The transponder is designed to present a larger electronic target than the aircraft from which it is deployed and thereby attract the weapon away from the aircraft.
In those deployment systems in which the towed vehicle is electrically interfaced to the aircraft, the electronic data transmission between the towed vehicle and aircraft is typically facilitated via the tow line used to interconnect the towed vehicle to the aircraft. Data transmitting tow lines as currently utilized generally comprise a core of standard conducting material extending throughout the tow line forming an electrical communication line between the towed vehicle and the aircraft. As the programming of anti-aircraft weaponry becomes more sophisticated to better discriminate between decoys and aircraft, the need to provide decoys within enhanced electrical capabilities similarly evolves. Additionally, as fighter weaponry becomes more advanced, it is likewise necessary to supply targets with enhanced data transmission and receiving capabilities. Thus, it is increasingly necessary for the tow line to transmit greater amounts of data and to conduct such transmission at a faster rate.
Further electrical conducting materials as currently utilized in data transmitting tow lines are highly susceptible to RF (radio frequency) interference which diminishes the data transfer capability of the tow line. It has been found that the shortcomings of conventionally known data transmitting tow lines can be overcome through the use of a tow line having a fiber optic core to establish the communications link between the aircraft and the towed vehicle. Such a fiber optic link has the advantage of providing enhanced data transmission rates as well as eliminating susceptibility to RF interference.
Though some aerial towed targets as currently manufactured are intended to be sacrificial, i.e. non-recoverable, others are intended to be recoverable. As can be appreciated, decoys by their very nature are intended to be sacrificial only, i.e. the tow line is cut at the aircraft at the end of a flight or mission. Though decoys and certain varieties of aerial towed targets are sacrificial, the need for rapid and reliable data exchange between these towed vehicles and the aircraft is of utmost importance for the reasons as previously discussed.
With regard to both recoverable and sacrificial towed vehicles, perhaps the most critical stage in the utilization of such towed vehicles lies in their initial deployment. The difficulty regarding deployment lies in the fact that the tow line must be able to withstand the extreme amount of tensile force exerted thereon by the drag of the vehicle and the rapid deceleration at the end of the payout of the vehicle. In one currently known deployment technique, the tow line is wrapped or folded at either the aircraft end or the towed vehicle end and allowed to pay out freely without braking. This particular deployment technique is primarily used in conjunction with sacrificial towed vehicles. In using this particular technique, the elasticity of the tow line must absorb the kinetic energy arising from the relative velocity of the towed vehicle to the aircraft at the end of the towed vehicle payout. As can be appreciated, oftentimes the tow line will snap during deployment, rendering the towed target or decoy irretrievably lost. Additionally, this particular deployment technique is only effective at relatively low aircraft speeds since at higher aircraft speeds, the mass of the tow line itself prevents full use of its elasticity which typically results in line failure at the end of the payout. Additionally, this particular technique does not lend itself to the transmission of power and electronic information through the tow line, the importance of which has been previously discussed. Since the tow line must possess such a high degree of elasticity so as not to snap, the line itself will typically cause the conductors within it to fail when it stretches. Thus, a tow line having a fiber optic core could not be used since the tow line elasticity would cause a failure of the fiber optics when the vehicle is deployed.
A second technique of deploying both sacrificial and recoverable towed vehicles involves the fixing of spools at either the aircraft or the towed vehicle to control the payout and braking of the tow line. In this respect, the tow line is wrapped about the spool and allowed to be payed out in a controlled manner. An example of a first deployment system which is operated in this manner and intended to be used in conjunction with sacrificial towed vehicles (i.e. decoys) is shown in United States Letters Patent No. 4,852,455 to Brum. In this particular system, the decoy is initially stored within a canister which is permanently attached to the aircraft. The canister includes a spool rotatably connected thereto about which the tow line is wound. The decoy is released from the canister via an explosive charge, and payed out behind the aircraft through the rotation of the spool. Centrifugal brakes are provided within the canister to oppose the rotation of the spool and thereby regulate the reeling payout speed of the deployed tow line. The tow line is adapted to communicate electrical signals to the decoy to regulate the operation of the electrical circuitry disposed therein. Electrical signals which are intended to be passed to the decoy through the tow line are communicated to the canister via one or more pin connectors. The pin connectors are interfaced to complimentary dynamic slip rings which are interfaced to the spool and tow line in a manner operable to transfer the electrical signals from the aircraft to the tow line and hence the decoy.
A second type of deployment system which utilizes the second technique and is used primarily with recoverable aerial targets comprises a bi-directional reeling machine. Examples of such reeling machines are shown in United States Letters Patent Nos. 4,770,368 to Yates et al.; 2,760,777 to Cotton; 2,778,584 to Wilson; 2,892,599 to Baldwin et al.; and 2,751,167 to Hopper. Such reeling machines typically utilize electric motors, as well as other types of supplementary power devices and brakes which are interfaced to a spool in a manner operable to reel equipment in and out from an aircraft. Additionally, some of these reeling machines are powered by means of an air driven turbine interfaced to a spool which can take advantage of the available power produced by the ram air energy impinging upon the device during aircraft flights. The aforementioned references all comprises reeling systems which are adapted to be permanently affixed to the aircraft. With regard to the paying out of the towed vehicle, the Cotton, Wilson and Baldwin references all disclose fixed pitch turbine blade design concepts with various means of throttling the air mass flow through the turbine in order to solely control the reel in rate and not the reel out rate of the towed vehicle. In this respect, Cotton controls reeler payout by means of a motor applied friction brake while Wilson and Baldwin rely upon centrifugally applied friction brakes to control reel out rate or speed which function in a manner substantially identical to that as previously discussed with respect to the Brum reference. The Hopper reference discloses a variable pitch turbine in which the blades of the turbine may be rotated to various attack angles to provide torque for reel in or provide opposing torque for reel out applications. However, this variable pitch turbine blade design is extremely expensive and requires constant operator monitoring of turbine speed and hence, has not been widely utilized in the prior art. The alternative disclosed in Hopper, i.e. having a fixed pitch turbine coupled to a reversing gear train to achieve reel in, reel out bi-directional operation give rise to the complexity of a reversing gear train which has likewise prevented the design's widespread use.
It will be appreciated that the aforementioned bidirectional reeling devices adapted to reel in and reel out towed vehicles are generally not used in conjunction with sacrificial vehicles in that there is typically no need to reel in a sacrificial vehicle. To the extent that these devices are used with towed vehicles requiring an electrical interface to the aircraft, electrical transfer mechanisms similar to that previously discussed with regard to the Brum reference, i.e. slip rings, are typically incorporated into these devices for purposes of conducting electrical data transfer.
Though the unidirectional and bi-directional reeling devices are operable to pay out the towed vehicle at a controlled rate, the use of slip rings for data transmission purposes does not lend itself to the use of tow lines incorporating fiber optics. Thus, the aforementioned reeling devices are not typically able to provide the enhanced data transmission capabilities facilitated by a fiber optic link. Such reeling devices also require high amounts of maintenance to insure the proper functioning of the braking mechanisms. Additionally, the use of such reeling devices necessitates the permanent affixation of a spool and brake assembly to the aircraft.